Hereinafter, a general frame structure being used in a wireless access system will be described.
FIG. 1 illustrates a frame structure being used in a broadband wireless access system (e.g., IEEE 802.16).
Referring to FIG. 1, a horizontal axis of the frame indicates an Orthogonal Frequency Division Multiple Access (OFDMA) symbol in time units, and a vertical axis of the frame indicates logical numbers of a sub-channel in frequency units. In FIG. 1, one frame is divided into data sequence channels during a predetermined time cycle period based upon the physical characteristics of the frame. More specifically, one frame consists of one DownLink Subframe and one UpLink Subframe.
At this point, the DownLink Subframe may include a preamble, a Frame Control Header (FCH), a DownLink map (DL-MAP), an UpLink map (UL-MAP, and at least one or more data bursts. Furthermore, the UpLink Subframe may consist of at least one or more UpLink data bursts and ranging sub-channels.
As shown in FIG. 1, the preamble, which corresponds to a specific set of sequence data positioned in the first symbol of each frame, is used to synchronize a terminal with a base station or to estimate a channel. The FCH is used to provide channel allocation information associated with the DL-MAP and information on channel codes. The DL-MAP/UL-MAP respectively corresponds to a Medium Access Control (MAC) message that is used to notify channel source allocation to the terminal. Furthermore, the data burst indicates a unit of the data being transmitted to the terminal from the base station or to the base station from the terminal.
A Downlink Channel Descriptor (DCD) that may be used in FIG. 1 represents an MAC message for notifying the physical characteristic in the DownLink channel, and an UpLink Channel Descriptor (UCD) that may be used in FIG. 1 represents an MAC message for notifying the physical characteristic in the UpLink channel.
Referring to FIG. 1, in case of the DownLink, the terminal detects the preamble being transmitted from the base station, so as to establish the synchronization with the base station. Thereafter, the UpLink map may be decoded by using the information acquired from the Frame Control Header (FCH). The base station may use a DownLink map or an UpLink map (DL-MAP/UL-MAP), so as to transmit scheduling information for Downlink or Uplink source allocation information to the terminal for each frame (e.g., 5 ms).